An electronic device may be provided with wireless circuitry. The wireless circuitry may include one or more antennas. The electronic device may have a housing in which control circuitry and radio-frequency transceiver circuitry is mounted. The transceiver circuitry may be used to transmit and receive radio-frequency signals using the antennas. The electronic device may have radio-frequency sensors. The radio-frequency sensors may include current sensors, voltage sensors, power sensors, sensors with taps and switching circuitry that tap signals flowing in a signal path and that may make measurements such as impedance measurements, and radio-frequency sensors with sensor antennas and associated sensor circuits that measure radio-frequency signals received using the sensor antennas. The control circuitry may make wireless circuit adjustments based on measured radio-frequency signals.